Method of signalling in an integrated access and backhaul network

ABSTRACT

The present invention relates to a method of signalling in an Integrated Access and Backhaul (IAB) network. The method comprises signalling information related to multiplexing capability and supported modes of operation from the child IAB node to the parent IAB node. An active mode of operation is determined at the child IAB node. The configuration to operate in the active mode of operation is signalled to the child IAB node. Timing Advance (TA) for each active mode of operation, guard information for each active mode of operation are signalled as configuration for the active mode of operation. Further, the method comprises signalling exchanges for fallback from one mode of operation to another at child IAB nodes.

CROSS-REFERENCE TO RELATED APPLICATIONS

The application is a continuation of U.S. patent application Ser. No.17/359,703, filed Jun. 28, 2021, which claims priority to Indian PatentApplication No. 202041027614, filed Jun. 29, 2020, the entiredisclosures of both of which are hereby incorporated by reference as ifset forth in their entirety herein.

FIELD OF THE INVENTION

The present invention relates to a signalling aspect, and moreparticularly to signalling aspects in an Integrated Access and Backhaul(IAB) network.

BACKGROUND OF THE INVENTION

The increase in the demand of high data rates has led to the usage ofmillimeter wave (mmWave) spectrum where huge bandwidth is available tosupport higher data rates. However, one of the main shortcomings ofmmWave is that it suffers high attenuation and hence cannot provide alarge cellular coverage. As a result, the cell size decreases andnumerous small cells are required to cover a certain area. As the numberof cells increase, it is not possible to connect every base station tothe core network using a wired link. In such a scenario, wirelessbackhaul is a promising solution. Such a network with wirelessbackhauling is known as an Integrated Access and Backhaul (IAB) Network.

An IAB network consists of a donor node 116, a set of TAB nodes, and aset of access UEs 102, 104, 106, 108. The donor node 116 has aconnection to the core network whereas the IAB nodes are connected tothe core network through donor node 116. The IAB nodes are connected todonor through wireless backhaul. The entire network operates under thecontrol of the donor node 116. Multi hop scenario is also possible,where IAB nodes attached to the donor node 116 have further child nodesand so on. Any given IAB node in the network has a parent node which maybe the donor node 116 itself or some other IAB node. Similarly, an IABnode in the network may also be a parent node to its child IAB nodes.Both donor and IAB nodes in the network can have their own access UEs102, 104, 106, 108.

A donor node 116 has a central unit (CU) and a distributed unit (DU).The CU can be in the donor node 116 or at some centralised location. TheCU controls the entire IAB network, whereas DU act as parent node forthe child nodes and access UEs 102, 104, 106, 108 connected to donornode 116. An IAB node has mobile terminal (MT) unit which is connectedto the parent node through parent backhaul link and a DU which isconnected to the child nodes through child backhaul link, and the accessUEs 102, 104, 106, 108 through access link. The available resources foran IAB node are shared among MT and DU of an IAB node for communicatingin backhaul and child/access links. FIG. 1 illustrate the basicdeployment of an IAB network with one donor node 116 and, a set of IABnodes and UEs 102, 104, 106, 108.

For the IAB network to operate, it is necessary to have certainsignalling exchange between the parent and child nodes since theoperation of the child node is controlled by the parent node. For e.g.,the way the resources shared between the MT and DU of child node dependson the hardware capability of the child node and resource configurationssignalled by the parent and donor nodes 116.

It is therefore desirable to provide certain signalling exchangemechanism due to which the resource details should be exchanged betweennodes in an IAB network.

SUMMARY OF THE INVENTION

The present invention relates to signalling in an Integrated Access andBackhaul (IAB) network.

An aspect of the present invention relates to a method of signalling inan Integrated Access and Backhaul (IAB) network. The method comprisessignalling, from a parent IAB node to a child IAB node, informationrequired for association of the child IAB node with the parent IAB node.The information required for association includes at least one of i) atleast one of multiplexing capability, hop order, number of child IABnodes associated, outage probability, and interference and load of theparent IAB node, and ii) a joint metric calculated by the parent IABnode based on at least one of the multiplexing capability, the hoporder, the number of child IAB nodes associated, the outage probability,and the interference and load of the parent IAB node. The method furthercomprises reporting, either separately or jointly, information relatedto the multiplexing capability and supported modes of operation from thechild IAB node to at least one of a Central Unit (CU) of a donor nodeand the parent IAB node. The reporting is done by a DU of the child IABnode to the CU of the donor node through an F1-AP interface, and by a MTof the child IAB node to a DU of the parent IAB node. The reporting isalso done by the DU of the child IAB node to the CU of the donor nodethrough the F1-AP interface. The CU of the donor node forwards theinformation related to the multiplexing capability and the supportedmodes of operation to the DU of the parent IAB node through the F1-APinterface.

In one aspect, the information required for association is used by thechild IAB node to calculate the joint metric. In one aspect, parent IABnode signals the joint metric along with the multiplexing capability tothe child IAB node.

In one aspect, an active mode of operation is determined at the childIAB node by one of the donor node, the parent IAB node and the child IABnode. Further, at least one of several actions are performed. Suchactions include a) exchanging information regarding switching from oneactive mode to another active mode, b) exchanging information regardingdefault mode, c) exchanging information related to Timing Advance (TA)for each active mode of operation, d) exchanging information related toguard time for each active mode of operation, and e) exchanginginformation related to In-Band Full Duplexing (IBFD) mode of operation.

In one aspect, the active mode of operation of the child IAB node isdetermined by the donor node based on the at least one of multiplexingcapability and supported modes of the child IAB node, multiplexingcapability, supported modes, and resource configuration of the parentIAB node, and network conditions.

In one aspect, the active mode of operation of the child IAB nodedetermined by the donor is communicated to at least one of the parentIAB node and the child IAB node.

In one aspect, the active mode of operation of the child IAB node isdetermined by the parent IAB node based on at least one of multiplexingcapability and supported modes of the child IAB node, resourceconfiguration of the DU of the child IAB node, and active mode ofoperation of the parent IAB node.

In one aspect, the active mode of operation is derived by the child IABnode by one of explicit signalling from one of the donor node and theparent IAB node, and implicitly based on at least one of resourceconfiguration of MT and DU of the child IAB node, multiplexingcapability of the child IAB node, supported modes of the child IAB node,and additional information including TA and guard period received fromthe parent IAB node.

In one aspect, the duration of the active mode of operation is signalledby the parent IAB node to the child IAB node.

In one aspect, the active mode of operation at the child IAB node is adefault mode when information regarding a switch from one active mode toanother active mode is not received by the child IAB node from theparent IAB node.

In one aspect, the default mode is signalled to the child IAB node bythe parent IAB node.

In one aspect, the TA signalled from the parent IAB node to the childIAB node depends on at least one of the active mode of operation of theparent IAB node, the active mode of operation of the child IAB node, andtiming of UL reception at the parent IAB node.

In one aspect, an offset to the TA is signalled from the parent IAB nodeto the child IAB node.

In one aspect, the TA is updated by initiating a RACH procedure andupdating TA value corresponding to a new mode of operation in RAR when amode switch happens. Alternatively, the TA is updated by signalling theTA values corresponding to a new mode of operation by the parent IABnode to the child IAB node, when the active mode of operation isswitched by at least one of the parent IAB node and the child IAB node.The TA is also updated by signalling a set of TA values for all possiblemodes of operation for a time frame from the parent IAB node to thechild IAB node.

In one aspect, guard information for each active mode includes guardsymbols. The guard symbols depends on resource configuration of MT andDU of an IAB node, propagation delay in a backhaul link of the IAB node,Downlink (DL) to Uplink (UL) and UL to DL switching time required at theIAB node, TA used for Uplink Transmission (UL-Tx) at the IAB node, and atiming of Uplink Reception (UL-Rx) at the IAB node, wherein the timingof UL-Rx depends on an active mode of operation of the IAB node and itschild IAB node. The TA used for UL-Tx depends on an active mode ofoperation of the IAB node and its parent node.

In one aspect, exchanging guard information includes signalling theguard information for all possible modes of operation from the parentIAB node to the child IAB node. Exchanging the guard information mayalso include signalling the guard information corresponding to a newmode of operation by the parent IAB node to the child IAB node, when theactive mode of operation is switched by at least one of the parent IABnode and the child IAB node.

In one aspect, to prevent overlap between resources at MT and DU of thechild IAB node when the DU of the child IAB node is configured as F,signalling of guard information comprises:

a) the parent IAB node inserting guard at the MT of the child IAB nodeassuming resource configuration of F resource at the DU of the child IABnode as the one corresponding to maximum guard duration,b) the parent IAB node inserting guard at the MT of child IAB nodeassuming resource configuration of F resource at the DU of the child IABnode as the one corresponding to minimum guard duration,c) the parent IAB node inserting guard at the MT of child IAB node basedon the dynamic configuration of the F resource at the DU of the childIAB node, wherein the child IAB node signals the dynamic configurationof the F resource to the parent IAB node; andd) the child IAB node dynamically configuring F resource at the DU suchthat guard is inserted at the start or end of the F resource to avoidoverlap with MT. The F resource is at least one of uplink, downlink, andguard.

In one aspect, when there is overlap between MT and DU of the child IABnode and the DU of the child IAB node is configured as soft resource,signalling of guard information comprises:

e) parent IAB node configures guard only when explicit IA is given forsoft resource at the DU of the child IAB node andf) the child IAB node configures guard at least one of start and end ofthe soft resource, when implicit IA is derived for the soft resource.

In one aspect, signalling of guard information comprises parent IAB nodeconfiguring the guard at MT of child IAB node based on the guardinserted at DU of the child IAB node which is signalled by the child IABnode to the parent IAB node and the guard required at MT of the childIAB node which is signalled by the child IAB node to the parent IABnode.

In one aspect, the child IAB node evaluates the guard required at MT ofthe child IAB node based on the guard present in DU of the child IABnode.

In one aspect, the signalling exchanges for IBFD mode of operationcomprises the child IAB node informing the parent IAB node about theIBFD capability of at least one of MT and DU of the child IAB node.

In one aspect, the signalling exchanges for IBFD mode of operationcomprises two parent nodes exchanging resource configuration informationfor proper scheduling of an IBFD capable User Equipment (UE) when the UEsimultaneously connects with the two parent nodes with Half Duplex (HD)capable DUs.

In one aspect, exchanges regarding at least one of switching mode ofoperation and interference measurement are signalled. The signallingexchange for interference measurement comprises the child IAB noderequesting a measurement guard period to the parent IAB node. The guardperiod is one of periodic and aperiodic, and is requested in terms ofone of absolute time and number of symbols.

In one aspect, periodicity of the guard period is requested in terms ofone of absolute time, number of symbols, number of slots, number ofsubframes, and number of frames. In one aspect, the signalling exchangesfor switching mode of operation comprises the child IAB node requestingthe parent IAB node for switching to a different mode of operation.

In one aspect, the child IAB node switches to the different mode ofoperation on receiving grant from the parent IAB node.

In one aspect, exchanges are signalled for switching mode of operationcomprises the parent IAB node signalling to the child IAB node grant formode switching and necessary parameters associated with the new modewherein the parameters are at least one of TA, guard, and measurementguard period.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings are included to provide a furtherunderstanding of the present disclosure, and are incorporated in andconstitute a part of this specification. The drawings illustrateexemplary embodiments of the present disclosure and, together with thedescription, serve to explain the principles of the present disclosure.

FIG. 1 illustrates an IAB network including IAB nodes and UserEquipment, in accordance with an embodiment of the present invention.

FIGS. 2 a and 2 b illustrate transmission and reception patterns invarious modes of operation of an IAB node, in accordance with anembodiment of the present invention.

FIG. 3 illustrates transmission and reception patterns in various modesof operation of an IAB node, in accordance with an embodiment of thepresent invention.

FIG. 4 illustrates transmission and reception patterns in various modesof operation of an IAB node, in accordance with an embodiment of thepresent invention.

FIG. 5 illustrates transmission and reception patterns in various modesof operation of an IAB node, in accordance with an embodiment of thepresent invention.

FIG. 6 illustrates transmission and reception patterns in various modesof operation of an IAB node, in accordance with an embodiment of thepresent invention.

FIGS. 7 a and 7 b illustrate donor configuring mode of operation ofchild node, in accordance with an embodiment of the present invention.

FIGS. 8 a, 8 b and 8 c illustrate mode of operation of child nodeimplicitly determined based on the resource configuration of MT and DU,in accordance with an embodiment of the present invention.

FIG. 9 illustrates the timing of various operations at child node, inaccordance with an embodiment of the present invention.

FIG. 10 illustrates all possible transitions across slots at a childnode and associated overlap between slots, in accordance with anembodiment of the present invention.

FIG. 11 illustrates resource transition between MT and DU at child andgrandchild nodes, in accordance with an embodiment of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

As used in the description herein and throughout the claims that follow,the meaning of “a,” “an,” and “the” includes plural reference unless thecontext clearly dictates otherwise. Also, as used in the descriptionherein, the meaning of “in” includes “in” and “on” unless the contextclearly dictates otherwise.

Exemplary embodiments will now be described more fully hereinafter withreference to the accompanying drawings, in which exemplary embodimentsare shown. This disclosure may however, be embodied in many differentforms and should not be construed as limited to the embodiments setforth herein. These embodiments are provided so that this disclosurewill be thorough and complete and will fully convey the scope of thedisclosure to those of ordinary skill in the art. Moreover, allstatements herein reciting embodiments of the disclosure, as well asspecific examples thereof, are intended to encompass both structural andfunctional equivalents thereof. Additionally, it is intended that suchequivalents include both currently known equivalents as well asequivalents developed in the future (i.e., any elements developed thatperform the same function, regardless of structure).

FIG. 1 illustrates an IAB network including IAB nodes and User Equipment(UE), in accordance with an embodiment of the present invention. The IABnetwork includes UEs 102, 104, 106, and 108, TAB nodes 110, 112, and114, and a donor node 116. TAB node 110 is a child node of the donornode 116 and a parent node of the IAB node 112. The IAB node 112 is achild node of the IAB node 110. The communication link between the IABnode 110 and the IAB node 112 is a child link for the IAB node 110 and abackhaul link for the IAB node 112. The communication link between theIAB node 110 and the donor node 116 is a backhaul link for the IAB node110.

In one embodiment, the various signalling aspects related to theoperation of an IAB network are described. The abbreviations explainedbelow have been used throughout the invention.

IAB-MT: MT of IAB node

IAB-DU: DU of IAB node

Parent-MT: MT of parent node

Parent-DU: DU of parent node

Child-MT: MT of child node

Child-DU: DU of child node

F: Flexible resources (Flexible resources are resources which can beconfigured to DL/UL/guard)

H: Hard (e.g., DU can use the H resource for transmission/receptionregardless of the MT's configuration)

S: Soft (e.g., DU can use the S resource for transmission/reception onlyif MT of child node does not transmit/receive in the resource,transmission/reception in MT of child node is not changed due to use ofthe resource by DU of child node or parent node signals indication ofavailability to use the S resource for transmission/reception in DU ofchild node)

NA: Not available (e.g., DU cannot use the resource fortransmission/reception in child/access link)

In one embodiment, multiplexing capability and supported mode ofoperation may be determined in the IAB network. The resources in whichan IAB node operates can be shared between IAB-MT and IAB-DU in time,frequency, space and code domain and are called Time DivisionMultiplexing (TDM), Frequency Division Multiplexing (FDM), SpaceDivision Multiplexing (SDM), and Code Division Multiplexing (CDM)respectively. In the case of TDM, any one link (MT or DU) will be activeat a given time instant. In the case of SDM/FDM, both MT and DU linkscan be active at the same time. However, some IAB nodes that supportSDM/FDM are subjected to Half Duplexing Constraint (HDC), where the nodecan either transmit in both the links or receive in both the links inthe same or different time-frequency resources. Certain IAB nodes canuse the same time-frequency resources for transmission in MT andreception in DU and vice versa and this is known as In Band FullDuplexing (IBFD). TDM, CDM, FDM, FDM with HDC, SDM, SDM with HDC andIBFD are known as the multiplexing capabilities of an IAB node. An IABnode can utilize these multiplexing capabilities for transmission andreception in backhaul and child/access links. The transmission andreception patterns followed in an IAB node are known as the modes ofoperation of the IAB node. Based on the multiplexing capability, the IABnode supports different modes of operation. The different modes possiblefor an IAB node are as follows.

Time Division Multiplexing (TDM)

Simultaneous Reception at DU and MT (SRxDM)

Simultaneous Transmission at DU and MT (STxDM)

DU receive and MT transmit (DURx_MTTx)

DU transmit and MT receive (DUTx_MTRx)

FIG. 2 to FIG. 6 illustrate the transmission and reception patterns invarious modes of operation of an IAB node. In FIG. 2 , IAB node 110 isin TDM mode of operation. In FIG. 2 a , only the MT of IAB node 110 isactive and is communicating with the donor node 116, whereas in FIG. 2 b, the DU of the IAB node 110 is communicating with access UE/MT of IABNode 112. In FIG. 3 , IAB node 110 is in SRxDM mode so that both MT andDU receive at the same time. This reception can be done in any of thebelow mentioned ways.

In the same time-frequency resources but different beams known asSpatial Division Multiplexing (SDM).

In the same time but different frequency resources on the same carrierknown as Frequency Division Multiplexing (FDM).

In the same time but different frequency resources on different carriersknown as Frequency Division Duplexing (FDD).

In FIG. 4 , IAB node 110 is in STxDM mode, where both MT and DU transmitsimultaneously. This transmission can be done in any of the belowmentioned ways.

In the same time-frequency resources but different beams, known as SDM

In the same time but different frequency resources on the same carrier,known as FDM.

In the same time but different frequency resources on differentcarriers, known as FDD.

In DURx_MTTx mode, the DU receives while the MT transmitssimultaneously, whereas in DUTx_MTRx mode, the DU transmits while the MTreceives simultaneously. These modes are possible in the following ways.

In the same time-frequency resources but different beams known as SDM.

In the same time but different frequency resources on the same carrierknown as FDM.

In the same time but different frequency resources on different carriersknown as FDD.

In the same time-frequency resources using IBFD capability.

As an example, in FIG. 5 , MT of TAB node 110 transmits and DU of TABnode 110 receives, whereas in FIG. 6 , MT of IAB node 110 receives andDU of IAB node 110 transmits.

The TDM is the simplest mode of operation and is the default mode ofoperation for an IAB node. However, for an IAB node with FDM/SDMcapability with HDC, simultaneous transmission and/or simultaneousreception is possible in addition to TDM mode depending on the resourceconfiguration of IAB-MT and IAB-DU, and the network conditions.Similarly, an IBFD capable node operates in DURx_MTTx and/or DUTx_MTRxmode in addition to TDM, STxDM and SRxDM modes depending on the resourceconfiguration at MT and DU, load, and interference levels. In the caseof unpaired spectrum with carrier aggregation (CA), separate carriersmight be assigned for IAB-MT and IAB-DU or for DL and UL, which makes itsimilar to paired spectrum. Similarly, each carrier in the pairedspectrum can be utilized like the single carrier of unpaired spectrum.Therefore, regardless of whether the spectrum is paired or unpaired, theIAB node can operate in any of these modes—TDM, STxDM, SRxDM, DUTx_MTRxor DURx_MTTx—if the mode is supported by the node.

In one embodiment, signalling of metrics from parent node to child nodemay need to be performed for association of the child node with theparent node.

In the conventional initial access process, the child node measures theReference Signal Received Power (RSRP) or Reference Signal ReceivedQuality (RSRQ) on Synchronisation Signal Block (SSB) transmitted by theparent node. The child node prefers a parent node with a higher value ofRSRP. However, in a multi-hop scenario with varying node capability,considering RSRP alone for initial attachment is not efficient. Forexample, a parent node with a high RSRP value may be serving a largenumber of child nodes, or having a higher hop order. A large number ofchild nodes results in high load, whereas the delay increases with thehop order. The latency associated with a parent node with IBFDcapability will be low compared to a parent node with TDM capability.Therefore, the selection of the parent node should be based on certainother parameters also, in addition to RSRP. Therefore, certainparameters should be signalled from the parent node to the child nodefor the child node to decide whether the parent node is suitable for itsrequirements. The parameters required for decision on latching needs tobe conveyed at the initial access stage itself or else it may result inmultiple parent node reselections. As an example, Table 1 provided belowshows the parameters (in addition to RSRP) to be considered in selectinga parent node. The parameters related to the parent node includemultiplexing capability, hop count, load, outage probability andinterference. In the case of multi-hop network, the RSRP should be thelowest RSRP over all the hops, the outage should be considered as theoutage of the weakest link across all the hops and the load to be takenas the maximum load among all the hops in the route between the CU tothe child node involving that particular parent node. Signalling theabove parameters about the parent node will be useful, especially incases like Ultra-Reliable Low Latency Communication (URLLC). Forexample, if both the child node and the parent nodes are IBFD capable,there will be latency reduction in the communication between them, asrequired for URLLC applications. Hence, the child node chooses itsparent node depending upon its multiplexing capability. Parametersmultiplexing capability and hop count are the properties of the nodewhereas load and interference are beam/frequency band dependent.Therefore, the mechanism for the indication of capability and hop countmay be different from the way load and interference are indicated.Signalling of a parameter associated with a parent node can be done inone or a combination of the following ways.

-   -   i. Using some reserved bits in Physical Broadcast Channel        (PBCH). There are some reserved bits in PBCH which can be used.    -   ii. Signalling in Remaining Minimum System Information (RMSI)        and Other System Information (OSI)    -   iii. Using RRC signalling. This is possible only after RRC        connection establishment.

Table 1 provided below mentions parameters which are signalled from theparent node to the child node.

Row Method number Parameter Signalling procedure 1 1 Multiplexingcapability 3 bit field 2 Hop order ceil(log2(maximum number possible)) 3Number of child nodes ceil(log2(maximum number associated possible)) 4Load a) The no. of associated child nodes is a direct indication of theload. b) The parent node can internally decide its load (high, medium orlow) based on some factors like traffic, child nodes etc. If b) isfollowed, then 2 bits can be given. 00-Low 01-Medium 10-High Or, 1 bitoptional field 0-Low 1-High No bit indicates load is medium. 2 5 Jointmetric of hop order, 0-Highly loaded number of child nodes and load1-Lowload calculated at the parent node

Two methods are considered in signalling the parameters associated witha parent node. In method 1, a parent node signals the parametersindependently to the child nodes, based on which child node formulate ajoint metric and is used in addition to RSRP in selecting the parentnode. In this method, a child node can assign weights to each parameterbased on its requirement. For example, a child node with URLLCrequirement assigns maximum weightage to the capability and hop count ofa parent node. As an example, the formula given below can be used tofind the joint metric at the child node. The child node calculates thejoint metric value for each possible parent node and compares it with apredefined threshold. The child node attaches to a parent node only ifthe joint metric value exceeds the threshold.

Joint metric=(Multiplexing capability)−(hop order)−(number of childnodes associated)−(load)

Multiplexing capability will have values from table 2:1 to 4

Hop order: 1 to maximum value

Number of child nodes: 1 to maximum value

Load: Values from table 1

In method 2, parent node evaluates the joint metric based on theparameters other than multiplexing capability and is signalled to childnode. For example, the parent node evaluates the joint metric based onthe equation given below and the metric is signalled to the child nodealong with multiplexing capability. The child node takes the decisionbased on this joint metric.

Joint metric=(hop order)−(number of child nodes associated)−(load)

In one embodiment, multiplexing capability and supported modes ofoperation may need to be signalled. The active mode of operation of theIAB node in a time instant is one of the modes supported by the IAB nodeand is determined based on resource configuration of MT and DU of theIAB node, active mode of operation of parent node and networkconditions. Parent-DU configures the resources to the child-MT, whereas,the CU configures the resources to the child-DU or the child-DU decidesits resource configuration. The multiplexing capability and thesupported modes of operation of the child node are crucial informationrequired at the donor and the parent nodes to configure resources to thechild node efficiently. For example, in the case of a child node withFDM/SDM capability and supporting STxDM mode, the CU configures thechild-DU as the DL and the parent-DU configures the child-MT as the ULso that both backhaul and child links will be active at the child node.Therefore, the child node signals its multiplexing capability and thesupported modes of operation to the donor and parent nodes. The donorand the parent nodes configure the resources to the child node based onits capability, supported modes of operation and the network conditionslike interference and load. The multiplexing capability and thesupported modes are directly signalled from the child-DU to the CUthrough F1-AP interface, whereas the multiplexing capability and thesupported modes are signalled from the child node to the parent node inthe below mentioned ways:

The child-MT communicates the capability and supported modes with theparent-DU directly through a Radio Resource Control (RRC) protocol.

The child-DU communicates the capability and supported modes to the CUthrough a F1-AP protocol. After receiving the capability and supportedmodes information from the child node, the CU informs the capability ofthe child node to the parent-DU through the F1-AP.

The multiplexing capability and supported modes of operation of thechild nodes are signalled using any of the following mechanisms.

Joint signalling: The multiplexing capability and supported modes aresignalled together. For example, a total of 3 bits are employed toconvey the multiplexing capability and supported modes of operation asmentioned in Table 2 provided below.

Signalling as independent entities: The multiplexing capability andsupported modes are signalled as independently. For example, if a singlebit is used to signal the capability of the child node as TDM andnon-TDM (FDM, SDM, CDM, IBFD), then the supported modes are signalledusing two bits as illustrated in Table 3 provided below.

TABLE 2 Joint signalling of capability and supported modes Row Signalnumber Capability Mode(s) bits 1 TDM Default (TDM) 00 2 FDM/SDM with HDDefault, SRxDM and STxDM 01 Constraint 3 FDM/SDM without Default, SRxDM,STxDM, 10 HD constraint DURx_MTTx and DUTx_MTRx 4 IBFD Default, SRxDM,STxDM, 11 DURx_MTTx and DUTx_MTRx

TABLE 3 Signalling of supported modes as separate entity Row numberMode(s) Signal bits 1 Default (TDM) 00 2 Default, SRxDM and STxDM 01 3Default, SRxDM, STxDM, 10 DURx_MTTx and DUTx_MTRx 4 Reserved 11

In one embodiment, an active mode of operation may be determined at thechild node. Once the capability/supported mode of operation of the childnode is known, the CU configures the resources to the child-DU based onthe capability of the child node, capability and configuration of theparent node, load in the network, interference level etc. Afterconfiguring the resources to the DU of the child node, the CU signalsthe resource configuration of the child-DU to the parent node. Now, theparent node configures the child-MT based on the resource configurationsof the parent-DU and the child-DU as well as the capabilities of theparent node and the child node. The active mode of operation of thechild node is determined by the resource configurations of MT and DU.For example, a child node with SRxDM capability works in that mode onlywhen the MT and DU are configured as DL and UL, respectively. Otherwise,the child node will operate in the TDM mode. There are two ways toconfigure the active mode of operation of the child node.

The active mode of operation of the child node is determined by thedonor node 116 based on the capability of the child node, capability andconfiguration of the parent node and network conditions. For example, achild node with advanced capability such as IBFD, is configured to workin the TDM mode when the load is low or when the interference is high.The resources are allocated to the child-DU based on the mode ofoperation. After configuring the resources to the child-DU, the donornode 116 informs the resource configuration of the child-DU to theparent node. Now, the parent node configures the child-MT so that thechild node works in the mode determined by the donor. Further, theparent can schedule an appropriate child node so that the parent nodecan work in the configured mode and enhance the network throughput. Forexample, when the parent node is working in the IBFD mode, the parentnode can schedule a child node working in the IBFD mode instead ofanother child node in the TDM mode, so that both BH and child links ofthe parent node will be active. The parent node determines the activemode of operation of the child node based on two mechanisms.

After configuring the resources to the child-DU, the donor explicitlyinforms the mode of operation of the child node to the parent node(through F1-AP) in addition to configuration of the child-DU. This isdone by control signalling from the donor to the parent node. As anexample, Table 3 can be reused here by the donor to indicate the mode ofoperation of the child node. Donor signal bits corresponding to row 1 inTable 3 if child node is configured to operate in TDM mode.

The parent node implicitly derives the active mode of operation of thechild node based on the capability of the child node and the resourceconfiguration of the child-DU. For example, if a child node has FDM/SDMcapability, support for STxDM and child-DU is configured as DL, theparent node derives the mode of operation of the child node as STxDM,and configures MT as UL for those set of slots. The advantage of thismethod is that no additional signalling is needed. However, implicitlyderiving the mode of operation leads to uncertainty in some scenarios.For example, consider a scenario in which a donor determines the mode ofoperation of a child node with IBFD capability as TDM because of networkconditions, and configures the resources to the child-DU accordingly. Inthis scenario, the parent node expects the child node to operate in FDmode based on the capability of the child node and configuration of thechild-DU. However, the child node (operating in TDM mode) cancommunicate in the backhaul depending on the H/S/NA configuration of theDU. Further, the child node requires indication of availability from theparent node to use the S resource for communication in the DU. Implicitdetermination of the mode can create ambiguity when the child-DU isconfigured as F. For example, the child node with FDM/SDM capability andsupport for STxDM mode can simultaneously transmit in MT and DU onlywhen the F resource at the DU is dynamically configured as DL, else thechild node operates in TDM mode. The parent node, which is unaware ofthe dynamic configuration of the F resource at the child-DU cannotderive the exact mode of operation of the child node when the child-DUis F.

An example of a donor configuring the mode of operation of a child nodeis illustrated in FIG. 7 . Consider the child node as having FDM/SDMcapability and supporting STxDM and TDM modes. The steps involved are asfollows.

Step 1: The CU configures the number of slots of the child-DU as DL sothat the child node works in STxDM mode followed by slots/symbols in TDMmode as shown in FIG. 7 a.

Step 2: The CU informs the configuration of the child-DU and the mode ofoperation of the child node to the parent node.

Step 3: The parent node configures the resources to the child-MT basedon the capability of the child node, configuration of the child-DU andthe mode of operation of the child node as shown in FIG. 7 b.

Step 4: The parent node and the CU are aware that the child node will bein STxDM and TDM modes within the frame. So they should signal TimingAdvance (TA) to be used in the BH link during STxDM and TDM mode ofoperation beforehand.

In one embodiment, the active mode of operation of a child node isdetermined by the parent node. The donor configures the resources to thechild-DU, but the donor does not decide its mode of operation. Theparent node knows the multiplexing capability and the configuration ofthe child-DU. Accordingly, the parent node assigns the resources to theMT of the child node. The mode of operation of the child node is decidedby the resource configuration of the child-MT and the child-DU. Forexample, if the slot of a child node with FDM/SDM capability andsupporting SRxDM mode is configured as UL for DU and DL for MT, the nodewill work in SRxDM mode, else the node will work in TDM mode in thatslot. The parent and the child nodes must have a common understanding ofthe mode of operation of the child node in each time slot and the timeinstances at which the mode switches from one mode to another, so thatthe parameters can be adjusted at the child-MT and the child-DU toachieve proper synchronization at the parent and the child nodes.Further, the mode of operation is required at the parent and child nodesto dynamically configure the F resource at the child-MT and thechild-DU, respectively. The child node determines its mode of operationbased on any of the two mechanisms described below.

The parent node explicitly signals the mode of operation to the childnode through RRC in addition to resource configuration of the child-MT.As an example, table 3 can be reused here by the parent node to indicatethe mode of operation of the child node to the child node. Signallingbits corresponding to row 1 can be used to indicate the mode ofoperation as TDM, whereas row 2 corresponds to SRxDM.

A child node implicitly derives the mode of operation based on itscapability and resource configuration and/or some additional signallinglike TA and guard period from the parent node. For example, if a childnode has FDM/SDM capability, supports STxDM mode and MT and DU of thechild node are configured as UL and DL, the child node derives its modeof operation as STxDM, based on the implicit approach. Otherwise, thechild node operates in TDM based on H/S/NA configuration of the DU.Information like TA and guard period are specific to a particular modeof operation. Thus, this information can also be used by the child nodeto decide its active mode. The advantage is that no explicit signallingis needed from the parent node to the child node in this method.However, the child node implicitly deriving the mode of operation canlead to uncertainty in some situations. For example, consider a scenarioin which a child node with IBFD capability is receiving a configurationfor MT and DU. The child node implicitly derives the mode of operationas FD, based on the capability, and transmits/receives in MT and DUirrespective of the H/S/NA configuration at the child-DU. However, thereare situations in which the child node with IBFD is expected to work inTDM because of the network conditions. Further, implicit determinationof the mode can create ambiguity when the child-MT is configured as F.For example, if the F resource at the MT is dynamically configured asUL, the child node supporting STxDM mode and DU configured as DL cansimultaneously transmit in MT and DU. Otherwise the child node operatesin TDM mode. Some resources assigned to the DU of the child node by thedonor can be flexible. In this case, the child-DU can decide by itselfwhether to transmit or receive in those F resources. The DU decides theconfiguration of the F resources depending on the resources configuredto the MT by the parent node, mode of operation of the child node beforeand after the F resource. The F resource at the DU is not configuredwith DL/UL when there is a mode switching. Further, the H/S/NAsignalling from the donor is considered only when the child node isoperating in the TDM mode.

An example of the mode of operation of the child node implicitlydetermined based on the resource configuration of MT and DU, isillustrated in FIG. 8 . In this example, a child node with FDM/SDMcapability and supporting STxDM and TDM modes is considered. The stepsinvolved are as follows.

Step 1: The CU configures the resources to the child-DU as illustratedin FIG. 8 a and informs the configuration of the child-DU to the parentnode.

Step 2: The parent node configures the child-MT based on the capabilityand the supporting modes of the child node, resource configuration ofthe child-DU and the resource configuration of the parent-DU as shown inFIG. 8 b.

Step 3: The parent node, aware of the resource configuration of thechild-MT and the child-DU, identifies the mode of operation of the childnode and signals TA to be used in the BH link during STxDM and TDM modesof operation.

Step 4: The child node determines the mode of operation and configures Fresource at DU of the child node accordingly. For example, in FIG. 8 c ,the initial portion of the H-F in slot 3 is configured as DL, so thatthe child node continues in the STxDM mode. Similar is the case with theF resources in the slots 7 and 9 in FIG. 8 c . Further, the H/S/NAconfiguration for the DU resource is considered only when operating inthe TDM mode, as indicated in FIG. 8 c.

The active mode of operation is required at the child node to signalnecessary parameters to the grandchild nodes and the access UEassociated with the child node. For example, a child node in SRxDM modesignals TA for its grandchild node and access the UE such that the UL-Rxaligns with the DL-Rx, whereas a child node in the TDM mode signals TAto the grandchild nodes and access UE such that the UL-Rx aligns withthe DL-Tx at the child-DU. The next section deals with the TAsignalling.

In one embodiment, Timing Advance (TA) may need to be signalled for eachactive mode of operation. Synchronization across hops is an essentialrequirement to avoid interference in multi-hop IAB network. In general,the synchronization conditions are 1) Downlink Transmission (DL-Tx) fromall the nodes in the network should be aligned and 2) Uplink Receptions(UL-Rx) from all the child nodes and access UE should align at theparent node. In addition, there are synchronization conditions dependingon the mode of operation of the node. The child IAB node sets atransmission time of MT to a transmission time of DU in the STxDM.Similarly, the parent IAB node sets a reception time of DU to areception time of MT in the SRxDM. Over The Air (OTA) synchronizationtechnique is employed to meet these requirements in an IAB networkwherein the parent node signals TA value to the child nodes to adjustthe UL-Rx at the parent-DU. The child nodes advance the transmissionfrom MT by the factor TA from the reception of the DL signal at the MT.Further, the child node derives the Time Difference (TDL) between thetransmission of a signal from the parent node and the reception of thesignal by the child-MT based on the TA value and adjust the transmissionfrom DU of the child node accordingly.

FIG. 9 illustrates the timing of various operations at a child node. T1denotes the propagation delay between the parent and the child nodes, TAdenotes the timing advance value signalled by the parent node, andTUL-Rx denotes the time difference between the DL-Tx and the UL-Rx atthe child node. The TA signalled by the parent node is a function of thepropagation delay between the parent node and the child node (T1), themode of operation of the child node, and the mode of operation of theparent node. For example, a parent node in TDM mode of operation signalsthe TA value to a child node as 2T1, whereas a parent node in SRxDM modeof operation signals the TA value to its child node as 2T1-T0, whereinTO is the propagation delay in the BH link of the parent node.Similarly, TUL_Rx at a child node depends on the mode of operation ofthe child node, and its grandchild node. For example, the UL and the DLreceptions should be aligned in a child node in the SRxDM mode so thatTUL_Rx=T1. Similarly, a child node in TDM/STxDM mode has TUL Rx=0,provided its grandchild can advance UL-Tx based on the TA valuesignalled by the child node. The child node updates the TA valuesignalled to the grandchild node to adjust the value of the TUL Rx,wherein this TA value is the minimum TA required when there is a modeswitch. In a practical scenario, there can be an offset to the minimumTA value as determined by the parent node and signalled to the childnode. For example, when the parent IAB node operates in SRxDM, then theparent IAB node signals conventional TA (i.e., TA=2T1) and an additionaloffset (i.e., T0), wherein the additional offset is used to align UL-Rxat DU of parent IAB node to DL-Rx at MT of parent IAB node.

Table 4 provided below illustrates the dependence of the TA valuesignalled by the parent node on the mode of operation of the parent andthe child nodes. As shown in table, there are 3 typical values for TAdepending on the mode of operation of the parent and child nodes.Whenever there is a mode switch at parent/child nodes, the correspondingTA value need to be signalled. However, if there is a mode switchresulting in a parent-child node combination not defined in the table,the TA value remains unchanged. In this case, no change in the TA valueis signalled as compared to the TA value in the previous mode ofoperation. Table 5 provided below illustrates the dependence of TUL-Rxon the modes of operation of the child and the grandchild nodes and thevalue of the TA signalled by the child node to achieve the requiredTUL-Rx. Whenever there is a change in the TUL-Rx at the child nodebecause of the mode switch at the child/grandchild node, the child nodemust signal the updated TA value to the grandchild node and thegrandchild node should adjust the UL-Tx accordingly.

TABLE 4 TA signalled by Cases Parent node Child node parent node 1 TDMTDM TA = 2T₁ 2 SRxDM TDM TA = 2T₁ − T₀ 3 TDM/SRxDM STxDM TA = T₁

TABLE 5 Grandchild TUL-Rx at TA signalled by Cases Child node node childnode child node 1 TDM TDM 0 2T₂ 2 SRxDM TDM T₁ 2T₂ − T₁ 3 TDM/SRxDMSTXDM T₂ T₂

A child node should receive updated TA from the parent, and shouldsignal new TA value to the grandchild node, before switching its mode.For example, child node switching from STxDM to TDM should receive TAupdate, from T1 to 2T1, from parent. Similarly, the child node shouldupdate the TA signalled to grandchild node from 2T2 to 2T2-T1 beforeswitching from TDM to SRxDM. Here, T2 denote the propagation delaybetween the child and the grandchild nodes. The various mechanisms usedby the parent node in signalling TA to its child node and child node tograndchild node is discussed next. Even though parent-child nodescenario is mentioned in the discussion, same is applicable between thechild and grandchild nodes as well.

The parent signals the TA value to the child node using two differentcommands depending on the situation. During initialization of the childnode, the parent evaluates the TA value based on the Random AccessChannel (RACH) preamble received from the child node and signals the TAvalue to the child node in Random Access Response (RAR). After initialaccess, the TA is updated using MAC-CE command, wherein the differencebetween the required TA and the existing value of TA is signalled by theparent. The TA value signalled by parent changes when the parent nodechanges its mode of operation between TDM/STxDM and SRxDM. Further, theparent must update the TA value when the child node switches the mode ofoperation between TDM/SRxDM and STxDM. The following methods can beemployed for updating the TA at the time of mode switching.

Initiating the RACH procedure at the time of mode switching and updatingthe TA value corresponding to new mode of operation in RAR

The TA values corresponding to each mode of operation is signalled bythe parent node to the child node at the time of mode switching usingMAC-CE signalling/DCI.

A set of TA values for different modes of operation in a time frame issignalled at the beginning.

The TA updation using the first two methods are difficult to implementas TA is signalled using RAR and MAC-CE signalling, which has longperiodicity of occurrence. However, the third method of TA updating canbe employed in which the modes for which the TA value for the child noderemaining the same are considered as a Timing Advance Set (TAS) and thecorresponding TA value is communicated to the child node using RAR andMAC-CE. The child node adjusts the uplink transmission timing based onthe current TAS, where the current TAS is communicated by the parentnode to the child node using RRC. Table 6 provided below illustrates theTAS needed based on the various modes of operation.

TABLE 6 Signalling Mode of bits TA set TA value Mode of Parent Child 00TAS1 2T₁ TDM/STxDM TDM/SRxDM 01 TAS2 2T₁ − T₀ SRxDM TDM/SRxDM 10 TAS3 T1with guard TDM/STxDM/ STXDM symbols SRxDM 11 Reserved — — —

In one embodiment, guard information for each active mode of operationmay need to be signalled. In some cases, the signalling TA value alonecannot ensure alignment of the UL-Rx from the child nodes at the parentnode. In that case, in addition to signalling the TA value, the parentnode must configure the guard symbols to align the UL-Rx from variouschild nodes and access UEs. For example, the child node in STxDM modemust align its uplink and downlink transmissions. Therefore, a childnode in STxDM mode cannot adjust its UL-Tx according to the TA signalledby the parent node and hence the parent node must configure the guardsymbols to align UL-Rx from the child node in STxDM mode. Further, themisalignment of various transmission/reception at a node results inoverlap between slots/symbols. For example, DL-Rx will be delayed bypropagation delay in BH link and overlaps with adjacent slot. FIG. 10illustrates all possible transitions across slots at a child node, andassociated overlap between slots. Figure covers the generalized scenarioin which the node works in different modes in two slots, and hence usedsubscript 1 and 2 to denote the timing in slot n and slot n+1,respectively. In figure, TUL-Tx denote the overlap of UL-Tx slot withthe previous slot and it depends on the TA value applied at the childnode as TUL-Tx=TA-T1. From figure it is clear that the resource overlapacross slots occur 1) with in MT of the child node 2) with in DU of thechild node and 3) between child-MT and child-DU. Further, there exist atime delay in switching from transmission to reception, and vice versain IAB nodes and is known as transmission-reception switching time (Ts).In many cases, resource overlapping across slots is not intended andcreates issues. For e.g., child node in TDM mode is configured withDL-Rx in slot n and DL-Tx in slot n+1, then DL-Rx overlap with DL-Tx atthe boundary. However, either MT or DU can be active at a time in TDMmode of operation. Therefore, either MT or DU should stoptransmission/reception during the overlapping portion.

The guard period required at child node for each switching case dependson the resource overlap, which depends on propagation delay in backhaul,child and access links of the child node, TA value applied for UL-Txfrom the child node, and the timing of UL-Rx at the child node. From thediscussions in Table 4 and Table 5 it is clear that the timing of UL-Txat the child node depend on the mode of operation of the parent andchild nodes, whereas the timing of UL-Rx at the child node depend onmode of operation of child and grandchild nodes. Based on FIG. 10 , theguard period required in switching from one resource configuration toanother across slots is evaluated and tabulated in Table 7 providedbelow. The table indicates the generalized expressions of guardduration, in terms of Ts, T1, TA and timing of UL-Rx at child node. Thetypical value of guard duration is obtained by evaluating the values ofTA and TUL-Rx from Table 4 and Table 5, respectively based on the modeof operation of parent, child and grandchild nodes across the slots.However, in practical scenarios, the guard duration can be more than thevalues tabulated in Table 7. For e.g., child node operating in SRxDMmode and, MT and DU are configured as DL and UL, respectively in slot n,then resource configuration of both MT and DU in slot n overlap withslot n+1. If DU of the child node is configured as DL-Tx in slot n+1,then guard is required at MT and DU of the child node at the end of slotn. From table, the guard required for DL-Rx to DL-Tx transition isTs+T1, whereas for UL-Rx to DL-Tx is Ts+TUL-Rx1. Since child node is inSRxDM mode for slot n, the value of TUL-Rx1 is obtained from Table 4 asT1. Therefore, both child-MT and child-DU insert guard period of Ts+T1at the end of slot n.

TABLE 7 From To Guard duration DL-Rx DL-Rx 0 UL-Tx T_(s) + TA₂ DL-TxT_(s) + T₁ UL-Rx Max (T₁ − T_(UL-Rx2), 0) UL-Tx DL-RX Max(T_(s) − TA₁,0) UL-Tx Max(TA₂ − TA₁, 0) DL-Tx Max(T₁ − TA₁, 0) UL-Rx Max(T_(s) −TA₁ + T₁ − T_(UL-Rx2), 0) DL-Tx DL-RX Max(T_(s) − T₁, 0) UL-Tx Max(TA₂ −T₁, 0) DL-Tx 0 UL-Rx Max(T_(s) − T_(UL-Rx2), 0) UL-Rx DL-RxMax(T_(UL-Rx1) − T₁, 0) UL-Tx Max(T_(s) + T_(UL-Rx1) + TA₂ − T₁, 0)DL-Tx T_(s) + T_(UL-Rx1) UL-Rx Max(T_(UL-Rx1) − T_(UL-Rx2), 0)

Resource overlap occurs within child-MT, between child-MT and child-DU,and within child-DU. The overlap within child-MT is taken care by theparent node by any one of the following methods:

Adjusting the scheduling: While configuring resources for child-MT,parent node ensures enough F resources between overlappingconfigurations.

Configuring guard symbols at the beginning or end of slots.

For example, DL-Rx followed by UL-Tx will create overlap. In the formermethod, parent node ensures enough F symbols between DL-Rx and UL-Txslots of child-MT, to avoid such overlap. Whereas in the latter methodthe parent node configures enough guard symbols at the end of DL-Rx slotor at the beginning of UL-Tx slot to avoid overlap. Further, guard-basedmethod is employed to avoid overlap between child-MT and child-DU.Parent node, being aware of the mode of operation of child node and TAused by the child node for UL-Tx, insert guard symbols at child-MT, toavoid resource overlapping between child-MT and child-DU. For example,the parent node insert guard at the beginning of slot n+1 at child-MT,if slot n+1 is configured as UL-Tx for child-MT and slot n isDL-Tx/UL-Rx for child-DU. Similarly, the overlap within child-DU isavoided by child node itself, by adjusting the scheduling or byconfiguring guard symbols at the child-DU. For e.g., child node in SRxDMmode will not configure symbols at the end of slot n or inserts guard atthe end of slot n, if slot n and slot n+1 are configured as UL-Rx andDL-Tx, respectively. Since the number of guard symbols at the child-MTdepends on mode of operation of parent and child nodes, the parent andthe child nodes should reach an agreement on the required number ofguard symbols for each transition in each mode of operation, and theparent node should update the values before mode switching at eitherparent or child node. For example, four bits can be used to representall the possible transitions in Table 7, and the number of guard symbolsinserted by the parent node in each switching scenario is signalled bythe parent node in advance. Further overlapping cases is managed by thechild node itself.

Table 7 refers to resource switching scenarios associated with the childnode in semi-static case and corresponding guard requirement. Eventhough semi-static configuration of guard symbols mentioned above workswell in many cases, it leads to resource wastage in many scenarios.Further, table did not cover the resource switching associated withdynamic configuration of resources in child node. Consider the scenarioin which there is a MT to DU resource switching and DU is configured asF. Based on the discussion above, parent node configure guard symbols atChild-MT to avoid resource overlap between MT and DU. However, the Fresource at DU of the child node is dynamically configured by child nodeas DL/UL, and the guard requirement vary based on this dynamicconfiguration. For e.g., in case of DL-Rx to F transition at child node,guard required is Ts+T1 if F is configured as DL-Tx by Child-DU, whereasguard is max(0, Ts-TUL-Rx2) when F is configured as UL-Rx. The parentnode is unaware of the dynamic configuration of F resource and hencethere is uncertainty associated with guard insertion. Any one of thefollowing strategies can be employed to avoid uncertainty associatedwith resource transition involving F symbols:

Parent node assume resource configuration of F resource as the onecorresponding to maximum guard duration and inserts guard symbolsaccordingly. For e.g., for the DL-Rx to F resource transition, parentnode inserts guard symbols of duration, which is maximum of Ts+T1 andmax (0, Ts-TUL-Rx2).

Parent node assumes resource configuration of F resource as the onecorresponding to minimum guard duration and inserts guard symbolsaccordingly. For e.g., for the DL-Rx to F resource transition, parentinserts guard symbols of duration, which is minimum of Ts+T1 and max (0,Ts-TUL-Rx2).

Child node informs parent node about the dynamic configuration of Fresource and the parent node inserts guard based on the information.This scheme needs new signalling from child node to parent node toinform dynamic configuration of F resource.

Child node dynamically configures F resource and insert guard at thestart or end of F resource to avoid overlap with MT resource in adjacentslot. This may create issue when DU has to configure guard symbols atthe starting of DL-Tx slot, as the initial symbols of DL-Tx slot can beconfigured for control signalling (PDCCH)

In one embodiment, child node is in TDM mode and resource transitioninvolve DU resource which is configured S. In that case, the guardsymbols are required in adjacent slot of MT only when explicit IA isgiven by parent node or implicit IA is derived by child node to use Sresource at DU, where implicit IA is derived based on certainconditions. As parent node is involved in configuring guard andsignalling explicit IA, parent node configure guard only when explicitIA is given. However, implicit IA is derived by child node and isunknown to parent node, and hence, parent node cannot configure guardsymbols at Child-MT based on implicit IA. Therefore, child nodeconfigures guard symbols at start or end of slot at DU configured assoft, if there is resource overlap associated with S resource andimplicit IA is derived for the slot.

Parent node inserts guard symbols at the Child-MT when there is resourceswitching within MT or between child-MT and child-DU. Similarly, childnode inserts guard symbols at MT of grandchild node to avoid resourceoverlap within MT or between MT and DU of grandchild node. These two areindependent processes and can happen simultaneously, so that guardsymbols are inserted at child-MT and child-DU, leading to resourcewastage. For e.g., consider the scenario in FIG. 11 , where there isresource transition between MT and DU at child and grandchild nodes.Parent node insert guard at child-MT, denoted as Tg1, to avoid overlapwith child-DU in adjacent slot, whereas child node insert guard at thebeginning of UL-Rx slot, denotes as Tg2, to avoid resource overlap atgrandchild node. In figure, guard periods at the end of slot n and slotn+1 overlap, and both child-MT and child-DU is idle at the same time,leading to resource wastage. To avoid overlap of guard symbols andassociated resource wastage following solutions can be considered.

Child node signals the duration of guard symbols inserted at thechild-DU to parent node, and the parent node configure guard at child-MTsuch that the guard at MT and DU will not overlap

Child node evaluates the guard required at child-MT to avoid overlapbased on guard already present in child-DU, and dynamically informs theguard required at child-MT to parent node.

If guard at child-DU is higher than guard at child-MT, i.e., Tg1<Tg2 inFIG. 11 , then parent node need not insert any guard symbol at child-MT.On the other hand, when guard required at child-DU is lower than guardat child-MT, i.e., Tg1>Tg2 in FIG. 11 , then parent node inserts guardsymbol of duration which is difference of guard duration in child-MT andchild-DU, i.e., Tg1−Tg2. In the former method child node signals Tg2 andparent node evaluates the guard duration based on Tg1 and Tg2, whereasin the latter one child signals either 0 or Tg1−Tg2 to parent node basedon the relative magnitude of Tg1 and Tg2.

Table 8 provided below summarizes the possible signalling associatedwith child node in each mode switching operation. Each row is thecurrent mode of operation and each column represents the mode ofoperation the child node switches to. For e.g., 1st row and 2nd columnof the table describes the operations required when child node switchesfrom TDM to STxDM. In table, T1 denotes the propagation delay inbackhaul link of child node and T2 denotes the propagation delay betweenchild node and grandchild node/access UE. From the table, it is clearthat a number of signalling is involved between parent and child nodewhen either parent or child node switches its mode. Below mentioned twoapproaches could be used for the signalling

Parent node signals all parameters associated with new mode, i.e., modeof operation, duration of the mode, TA and guard values, a priori in thebackground. The child node makes necessary adjustments beforehand andswitches to new mode directly in the corresponding slot.

Child node stops transmission/reception in MT and DU before modeswitching. Parent node signals necessary information and child nodeupdates.

TABLE 8 TDM STxDM SRxDM IBFD TDM — Node has Node has Node is IBFD STxDMSRxDM capable capability & MT capability & MT Self- and DU are and DUare interference is configured as UL configured as manageable by and DL,DL and UL, the child node respectively respectively Child informs CUshould not CU should not CU that it can signal H/S/NA signal H/S/NAoperate in IBFD Parent node Parent node CU should not signals the newsignals the new signal H/S/NA to mode of mode of child-DU operation ofthe operation of the CU inform child node and child node and parent nodeabout the duration of the duration of non signalling of the new mode thenew mode H/S/NA Parent node Parent node Parent node update TA fromsignals updated signals the new 2T₁ to T₁ and guard table to mode ofinserts guard child node operation of the symbols in UL Child node childand the slots to achieve update TA to duration of the proper alignmentgrandchild/ new mode of UL-Rx at access UE from Parent node parent node2T₂ to 2T₂ − T₁ communicates Parent node with child-MT signals updatedirrespective of guard table to the H/S/NA child node configuration ofchild-DU Parent node signals updated guard table to the child node STxDMIBFD not — Node with Based on supported and SRxDM capability and RA RAviolates capability and, Parent node HDC MT and DU signals the new CUsignal configured as mode of H/S/NA DL and UL, operation of the CUinform respectively child and the parent node Parent node duration ofthe about H/S/NA signals the new new mode configuration of mode ofParent node child-DU operation of the signals updated Parent node childnode and guard table to schedule child- the duration of child MT basedon the the new mode Parent node H/S/NA Parent node update TAconfiguration of signals updated signalled to child child-DU guard tableto node from T₁ to Parent node child node 2T₁ signals the new Parentnode mode of updates TA operation of the signalled to child node andchild node from the duration of T₁ to 2T₁ the new mode Child node Parentnode update TA to update TA grandchild/ signalled to child access UEfrom node from T₁ to 2T₂ to 2T₂ − T₁ 2T₁ Parent node signals updatedguard table to child node SRxDM FD not Based on — Based on supported andcapability and capability and RA RA violates RA Parent node HDC Parentnode signals the new CU signal signals the new mode of H/S/NA mode ofoperation of the CU inform operation of the child and the parent-DUabout child node and duration of the H/S/NA the duration of new modeconfiguration of the new mode Parent node child-DU Parent node signalsupdated signals updated Parent node guard table to guard table tosignals the new child node child mode of Parent node child nodeoperation of the update the TA updates the TA child node and signalledto child signalled to the duration of from 2T₁ − T₀ to grandchild node /the new mode T₁ access UE from Parent node Child-DU 2T₂ − T₁ to 2T₂schedule child- updates the TA MT based on the signalled to H/S/NAgrandchild node / configuration of access UE from the child-DU 2T₂ − T₁to 2T₂ Parent node signals updated guard table to child node child nodeupdate TA signalled to grandchild/ access UE from 2T₂ − T₁ to 2T₂ IBFDChild node Based on Based on — cannot manage capability and capabilityand self-interference RA RA Minimize Parent node Parent nodeinterference signals the new signals the new when traffic is mode ofmode of low operation of the operation of the CU signal child node andchild and the H/S/NA the duration of duration of the CU inform the newmode new mode parent-DU about Parent node Parent node H/S/NA update theTA signals updated configuration of signalled from guard table tochild-DU 2T₁ to T₁ child node Parent node Parent node Child node signalsthe new signals updated update the TA mode of guard table to signalledto operation of the child node child node from child and the 2T₂ to 2T₂− T₁ duration of the new mode Parent node schedule child- MT based onthe H/S/NA configuration of child-DU Parent node signals updated guardtable to child node

In one embodiment, a mechanism for fallback is essential for IAB nodes.In one scenario, a child node operates in IBFD mode. Due to high amountof interference at the AC/BH link, the performance starts degrading.Hence, the child node cannot continue in IBFD mode and needs to switchto/fallback to the default mode. The child IAB node signals to theparent node and/or donor node to indicate that it wants to fallback todefault mode. This can be using RRC or uplink control information (UCI).The default mode is one of the modes supported by the child IAB node.The default mode can be the mode of operation desired by the child IABnode or configured by parent node. The parent node and/or the donorsignal switching grant to the child node, wherein the switching grant isthe active mode of operation and/or a new set of configurations for theactive mode of operation. The active mode of operation signalled inswitching grant can be the default mode of operation requested by thechild IAB node. Any other signalling like TA, guard period etc. can alsobe signalled or the child node can use the default table (as mentionedearlier) to begin its operation in default mode. However, the child nodecannot fallback by itself unless it receives switching grant whichallows it to fallback. This ensures that the final decision always lieswith the parent node. The child node continues to operate in its currentmode until it receives any control from the parent node. Even in IBFDmode, few resources are configured in a way such that there is defaultmode of operation (like few slots in TDM mode). This will ensure that,even if the child node does not receive any control informationregarding mode change from the parent node, it can operate in thedefault mode in these slots. If the parent node falls back to defaultmode from its current mode of operation, it will affect the UL/DLconfiguration, TA and guard period of the child node associated with it.Hence, the parent node must signal the new parameters to the child node.

In one embodiment, interference measuring occasions may need to besignalled for IBFD mode of operation. When an IAB node operates in IBFDmode, it requires to measure the self-interference (SI) periodically.For e.g., the DU measures the SI from the MT and vice versa. Duringmeasurement, the IAB node should only focus on the measurement and noother transmission/reception should take place apart from thetransmission/reception at the IAB node required to measure the SI.Hence, the MT of the IAB node requires to inform the DU of its parentnode (since it is under the control of the parent node) that BH linkshould be switched off for some time. During this time, the IAB nodeperforms its SI measurement. There are two ways to signal this asprovided below:

Signal the parent node (RRC or UCI) asking for a measurement guardperiod whenever required. The measurement guard period is in terms ofabsolute time or for a fixed number of OFDM symbols.

After exchange of multiplexing capability information, the IAB nodesignals the periodicity and duration of the measurement guard period(RRC) required to the parent node.

Other scenarios involving IBFD are described below. In one case, DU maybe Half Duplex (HD) capable and UE may be IBFD capable. In such case,the UE can transmit and receive in the same time-frequency resources.Thus, it performs UL and DL simultaneously. However, since the DU is HDcapable (either receive or transmit at a given time), the UE must beconnected to two parent node DUs at the same time to use its IBFDcapability. UE is configured with UL by one parent node and DL by other.Since, the UE is associated with 2 parent nodes, it receives resourceconfigurations from both the parent nodes. The resource configurationsare such that both UL and DL are allowed simultaneously at the UE. Theparent nodes communicate with each other to provide properconfigurations to the UE such that the resource configurations providedto the UE does not violate the capability of the UE. For e.g., if boththe parent nodes configure UL in the same time-frequency resources, theUE will not be able to perform this.

In another case, parent-DU may be IBFD capable (DUTx_DURx) and UE may beIBFD capable. In such case, the DU is capable of simultaneoustransmission and reception (DUTx_DURx). Since both are IBFD capable,there is no need for any configuration signalling at UE or DU.

In yet another case, MT may be HD capable and DU may be IBFD capable(DUTx_DURx). In such case, the IAB node supporting DUTx_DURx mode ofoperation, signals it to its parent node. Since the DU is IBFD capable,there is no need for a resource configuration for the DU to be given bythe donor. Depending on the multiplexing capability between the DU andthe MT and the resource configuration at MT, the DU can adjust itstransmission and reception. MT should receive resource configurationfrom the parent node.

In yet another case, MT may be IBFD capable (MTTx_MTRx) and DU may be HDcapable. In such case, the MT is capable of simultaneous transmissionand reception (MTTx_MTRx). Here, the DU receives a resourceconfiguration from the donor. The child-MT signals the parent node thatit is capable of supporting MTTx_MTRx mode of operation. If the MT isconnected to an IBFD parent-DU, then no resource configuration isrequired at the MT. The parent-DU knows the resource configuration ofthe child-DU and the multiplexing capability. Based on this, theparent-DU decides whether to transmit DL to the child-MT such that themultiplexing capability of the child node is not violated. For e.g., thechild node has only TDM multiplexing capability. The parent-DU shouldnot transmit to the child-MT in resources where the child-DU isoperating. However, if the MT is connected to a HD parent-DU, then MTwill receive a resource configuration from the parent node and operatein a HD mode.

In yet another case, MT and DU may both be IBFD capable. In such case,resource configuration is not required at the DU. However, MT willrequire a resource configuration if it is connected to a HD parent node.The child node signals MTTx_MTRx and DUTx_DURx supported modes ofoperation to the parent node.

In the above detailed description, reference is made to the accompanyingdrawings that form a part thereof, and illustrate the best modepresently contemplated for carrying out the invention. However, suchdescription should not be considered as any limitation of scope of thepresent invention. The structure thus conceived in the presentdescription is susceptible of numerous modifications and variations, allthe details may furthermore be replaced with elements having technicalequivalence.

We claim:
 1. A method of signaling in an Integrated Access and Backhaul(IAB) network, the method comprising: reporting, by at least one childIAB node, information to any one or more of a Central Unit (CU) of adonor node or a parent IAB node, wherein the information includes anyone or more of a multiplexing capability or supported modes of operationof the at least one child IAB node; and receiving, by the at least onechild IAB node, at least one configuration for operating in an activemode from the any one or more of the CU of the donor node or the parentIAB node, wherein the at least one configuration includes any one ormore of timing information or guard information.
 2. The method asclaimed in claim 1, wherein the multiplexing capability of the at leastone child IAB node includes any one or more of Time DivisionMultiplexing (TDM), Code Division Multiplexing (CDM), Frequency DivisionMultiplexing (FDM), FDM with Half Duplexing Constraint (HDC), SpaceDivision Multiplexing (SDM), SDM with HDC, or In Band Full Duplexing(IBFD).
 3. The method as claimed in claim 1, wherein the supported modesof operation of the at least one child IAB node includes one or more ofTDM, Simultaneous Reception at a Distributed Unit (DU) and a MobileTerminal (MT) (SRxDM), Simultaneous Transmission at DU and MT (STxDM),DU receive and MT transmit (DURx_MTTx), or DU transmit and MT receive(DUTx_MTRx).
 4. The method as claimed in claim 3, wherein the at leastone child IAB node sets a transmission time of MT to a transmission timeof DU in the STxDM.
 5. The method as claimed in claim 3, wherein the atleast one parent IAB node sets a reception time of DU to a receptiontime of MT in the SRxDM.
 6. The method as claimed in claim 1, whereinthe reporting is performed by one of: a DU of the child IAB node to theCU of the donor node through an F1-application protocol (F1-AP)interface, a MT of the child IAB node to a DU of the parent IAB nodeconnected to the parent IAB node, and the DU of the child IAB node tothe CU of the donor node via the F1-AP interface, wherein the CU of thedonor node forwards the information including any one or more of themultiplexing capability or the supported modes of operation to the DU ofthe parent IAB node via the F1-AP interface.
 7. The method as claimed inclaim 1, wherein the active mode is at least one mode from the supportedmodes of operation of the at least one child IAB node.
 8. The method asclaimed in claim 1, wherein the active mode of the at least one childIAB node is determined by one of the CU of the donor node, the parentIAB node and the child IAB node.
 9. The method as claimed in claim 1,wherein the active mode of operation is determined by the at least onechild IAB node by any one or more of: explicit signaling from one of thedonor node and the parent IAB node, or implicitly based on any one ormore of a resource configuration of a MT and DU of the at least onechild IAB node, multiplexing capability of the at least one child IABnode, supported modes of the at least one child IAB node, timinginformation or guard information.
 10. The method as claimed in claim 1,wherein the configuration comprises the active mode of the at least onechild IAB node in a time resource.
 11. The method as claimed in claim 1,wherein the timing information comprises one or more of a timing advance(TA) value and an offset.
 12. The method as claimed in claim 1, whereinthe timing information comprises an offset value when the parent IABnode sets a reception time of a DU to a reception time of a MT.
 13. Themethod as claimed in claim 11, wherein the child IAB node applies the atleast one offset to the TA value.
 14. The method as claimed in claim 1,wherein the timing information depends on any one or more of: an activemode of operation of any one or more of the child IAB node or the parentIAB node, reception time of parent IAB node, or transmission time of atleast one child IAB node.
 15. The method as claimed in claim 1, whereinthe guard information comprises at least one guard symbol, wherein theat least one guard symbol depends on timing of at least one oftransmission and reception of any one or more of the parent IAB node orthe child IAB node.
 16. The method as claimed in claim 1, comprisesrequesting, by the at least one child IAB node, a desired active mode ofoperation to at least one of parent node and CU of donor node,receiving, by the at least one child IAB node, a switching grant from atleast one of parent node and CU of donor node; and switching, by the atleast one child IAB node, to the desired active mode.
 17. The method asclaimed in claim 16, wherein the switching grant is any one or more ofthe active mode of operation or configuration for operating in theactive mode of operation.
 18. The method as claimed in claim 1, whereinthe multiplexing capability comprises IBFD capability of at least one ofMT and DU of the child IAB node.
 19. The method as claimed in claim 18,wherein the IBFD capability comprises simultaneous transmission andreception.
 20. The method as claimed in claim 1, wherein at least oneconfiguration comprises scheduling for measuring interference.
 21. Themethod as claimed in claim 20, wherein scheduling is in response to arequest from at least one child IAB node.
 22. The method as claimed inclaim 20, wherein the scheduling is one of periodic and aperiodic and isin terms of at least one of absolute time, number of slots, number ofsymbols, number of subframes, and number of frames.
 23. The method asclaimed in claim 1, comprises at least one of receiving, by at least onechild IAB node, an information required for association from a pluralityof IAB nodes, performing, by at least one child IAB node, initial accesswith at least one IAB node from the plurality of IAB node, based on theinformation; and establishing a connection with at least one parent IABnode from the plurality of IAB nodes.
 24. The method as claimed in claim23, wherein the information comprises at least one of: at least one of,hop order, at least one multiplexing capability, number of child IABnodes associated, outage probability, interference, and load of theparent IAB node, and a joint metric calculated by the parent IAB nodebased on at least one of, the hop order, the at least one multiplexingcapability, the number of child IAB nodes associated, the outageprobability, interference and load of the parent IAB node.
 25. Themethod as claimed in claim 1, comprises at least two parent IAB nodesexchanging resource configuration of one of User Equipment (UE) andchild IAB node when the one of UE and child IAB node simultaneouslyconnects with the two parent nodes.